This proposes to undertake a systematic examination of the psychological processes underlying the ways that people make quantitative judgments of sensory and perceptual magnitudes. In particular, the question is, What psychological representations and processes underlie psychophysical judgments both of magnitudes per se, and also of relationships between magnitudes -- that is, judgments of average magnitude, total magnitude, intervals of magnitude, and ratios of magnitude. Judgments will be made by magnitude-estimation and by rating (graphic-rating, category-rating) procedures. The goal is to distinguish (1) Scales -- the underlying psychologic values (sensory and perceptual scales of, for example, loudness, touch, temperature); (2) combinatorial rules for the task -- the rules describing the way psychological scale values combine for each of the relationships mentioned above; and (3) Procedures -- the way that the particular scaling procedure taps the combined scales values. An important question is whether, for a given sensory contiuum, the same psychological scale underlies combinatorial processes on different tasks. Accordingly, three models will come under special scrutiny. A simple model states that a single scale underlies judgments of magnitudes, totals, averages, intervals, and ratios. Another, more complex (hierarchical) model states that different scales underline different combinatorial processes. A third model states that for some tasks, the combinatorial processes operate not at the level of the psychological scale values, but instead at the level of the quantitative judgments themselves. All analyses will be performed at the level of individual subjects, in order to evaluate possible differences in scales and/or combinatorial processes.